We have found that approximately half of basal type breast cancers show evidence for autocrine activation of the EGFR by amphiregulin (AREG). Furthermore, our data indicate that when AREG is the activating ligand for EGFR, receptor trafficking and down stream signaling is dramatically altered resulting in the establishment of a positive feedback loop involving NF-B and IL-1, the expression of a distinctive transcription profile, and the acquisition of motile and invasive capacity. The over arching goal of the work proposed in this application is to elucidate how AREG fundamentally alters the biology of human breast cancer cells and contributes to the expression of phenotypes characteristic of aggressive human breast cancer, and to test the hypothesis that AREG's effects are mediated via activation of NF-B and IL-1. The specific aims of this project are: 1) To test the hypothesis that accumulation of EGFR at the cell surface, which occurs in AREG stimulated cells and not EGF-stimulated cells, is the proximate mechanism for the altered EGFR signaling that results in activation of NF-B and expression of IL-1, 2) To determine the components of the EGFR signalosome in AREG stimulated cells, to elucidate the signaling pathway from AREG-activated EGFR to the nuclear accumulation of NF-B, and to analyze the role of this pathway in the expression of aggressive growth phenotypes of basal breast cancer cells, 3) To determine how IL-1 signaling modulates EGFR tyrosine phosphorylation in breast cancer cells and mammary epithelial cells with an AREG/EGFR autocrine loop by influencing the activity of tyrosine phosphatases and/or tyrosine kinases that target EGFR, and 4) to determine if EGFR-inhibition in breast cancers with AREG/EGFR autocrine loops results in down- regulation of IL-1, and loss of nuclear of NF-kB. AREG activation of EGFR fundamentally alters the biology of HME cells and induces phenotypes expressed by highly aggressive and drug-resistant breast cancer cells. Understanding the mechanistic basis for this difference, and understanding the downstream consequences of AREG mediated activation of the EGFR will improve our understanding of the biology of a particularly aggressive subclass of breast cancer for which there are no therapeutic options beyond standard chemotherapy.